Forestry Methods

This page describes the different scientifically-proven methods applicable for cutting
to manage Oregon forests. These are time-proven forestry methods—known as “silvicultural
methods”— accepted by the professional Society of American Foresters (www.safnet.org).
These silvicultural methods are the range of methods suited for the many different
forest types across Oregon’s geographic regions.

Using appropriate terms for forestry and harvest methods helps to clearly communicate
these concepts among the people, organizations and agencies that prescribe and manage
Oregon forests. The use of common terminology provides a shorthand nomenclature
for prescribed harvest treatments, and for how these treatments will be managed
over the life of a forest.

“Silviculture” is defined as the science of managing forest vegetation by controlling
tree stand establishment, growth, composition, quality and structure, planned for
the forest resource objectives or the landowner.

A “silvicultural method” is a particular harvest treatment—either regeneration or
intermediate—implemented for the purpose of achieving the long-term stand and landowner
objectives. Silvicultural is a long-term process, which includes a program of different
treatments/cuttings that are planned for the entire life of the stand of trees—known
as the length of a rotation. A “stand” is a term describing an area of forest having
a common management goal. The appropriate silvicultural method is prescribed by
forestry professionals who tailor the method and timing to the specific biotic and
abiotic site conditions, which aim to accomplish an array of landowner management
objectives.

Commonly
used terms such as “partial cutting,” “selective logging,” “partial retention logging,”
or “restoration logging” are not specific silvicultural methods; rather they are
generic labels that simply describe cutting a portion of the trees in a forest stand.
Silvicultural prescriptions do not use generic harvesting terms such as “selective
cutting” or “partial cutting.”

Silvicultural harvest methods are classified into two general classes, based upon
the goal of the harvest:

Regeneration methods -- Goal is to begin establishment
of young new stand of tree seedlings (regeneration); to by removing a mature stand
at end of stand rotation length. In Oregon, the new young tree regeneration must
be “free to grow” and well distributed within 6 years after the regeneration cut.

Intermediate methods -- Goal is to modify the composition,
health and density of retained leave trees for continued stand development; occurs
at an “intermediate” time midway during stand rotation length. This method must
retain enough tree canopies to not trigger Oregon tree regeneration rules.

A regeneration
method is a harvest treatment or cutting procedure with the goal of a initiating
new forest crop of young tree seedlings, thereby establishing and creating a new
age class. The harvest treatment must open the forest canopy enough to allow young
native trees to establish and grow (many Oregon tree species demand open sunlight
to establish). The regeneration method is designed to remove a mature stand of trees
at its planned culmination—known as the rotation length. Depending on the specific
seedling establishment needs of the species and site, regeneration methods are grouped
into four categories: 1) even-aged; 2) two-aged; 3) uneven-aged; and 4) coppice.

Even-aged methods regenerate to establish and grow a stand with a single age class,
or one tree canopy layer. Clearcutting, seed tree, and shelterwood are the three
even-aged harvest methods proven to work in Oregon forest types. Many of Oregon’s
native conifer and hardwood species are shade intolerant, and young trees establish
and thrive under the open conditions of the even-aged management methods. “Salvage”
is a generic term—that can be incorporated into any even-aged method—when that regeneration
harvest includes cut and removal of dead or damaged trees from a wildfire, storm,
flood, disease, or pest attack.

Clearcutting

Clearcutting method is the cutting of all (or most) trees, producing an open and
fully-exposed microclimate for the establishment of a new forest crop of young trees,
or a new age class. Young tree regeneration can be from planted seedlings, natural
seeding, and/or pre-existing young trees. Cutting may be done in stands (over 3
acres in size), in strips, or small patches (2 acres).

Seed tree

Seed tree method is the cutting of all trees, except for a small number of widely
dispersed trees retained for seed production, species diversity, and/or structure.
This method produces a new forest crop of young trees, or a new age class in fully
exposed microenvironment. Young tree regeneration can be from planted seedlings,
natural seeding, and/or pre-existing young trees. All or some of the seed trees
are usually harvested & removed in a second ‘overstory removal’ treatment, after
a few years when regeneration becomes established (see Shelterwood).

Shelterwood (uniform)

Shelterwood method is the cutting of most trees, leaving those needed to produce
sufficient shade to produce a new forest crop of young trees, or a new age class
started in a moderated, partially-shaded, microenvironment. Young tree regeneration
can be from planted seedlings, natural seeding, and/or pre-existing young trees.
Shelterwood method can include a sequence of up to three separate cuttings: (a)
an optional preparatory cut to enhance conditions for seed production; (b) a shelterwood
(establishment) cut to initiate regeneration; and (c) an overstory removal cut to
release the young regeneration from competition with the overstory canopy. Shelterwood
offers options for the pattern of openings and shelter canopy created, including:
uniform shelterwood; group shelterwood; or irregular shelterwood (uneven pattern;
residual trees may be left a longer time, added non-timber objectives).

Two-aged methods regenerate to establish and grow a stand with two age classes,
or two tree canopy layers. The resulting stand may be two-aged or tend towards an
uneven-aged condition. These methods apply the same primary cutting techniques as
do the even-aged methods, except that the retention of a number of extra overstory
green trees left indefinitely for strategic purposes, such as structure, habitat,
shelter, aesthetics, and/or public policy. The consequence of this extra retention
is slower regeneration establishment and retaining a second age class of additional
overstory. “Salvage” is a generic term—that can be incorporated into any two-aged
method—when that regeneration harvest includes cut and removal of dead or damaged
trees from a wildfire, storm, flood, disease, or pest attack.

Clearcutting with Reserves – A clearcut, in which varying numbers
of canopy reserve trees are not harvested to attain goals other than regeneration.

Seed Tree with Reserves – A seed tree cut, in which some or all
of the seed trees are retained after regeneration has become established to attain
goals other than regeneration.

Shelterwood with Reserves – A shelterwood cut, in which some or
all of the shelter trees are retained after regeneration has become established
to attain goals other than regeneration.

Uneven-aged
methods regenerate to establish and grow a multi-aged stand, or three or more tree
canopy layers. These methods harvest and remove some trees in most size classes
either singly, in small groups, or in strips. Long-term management under this method
demands more frequent return harvest intervals, which are necessary to periodically
establish small amounts of new age classes and remove small numbers of trees from
other age classes. Many of Oregon’s native conifer and hardwood species are shade
intolerant and are not very conducive to management under uneven-aged methods. “Salvage”
is a generic term—that can be incorporated into any uneven-aged method—when that
regeneration harvest includes cut and removal of dead or damaged trees from a wildfire,
storm, flood, disease, or pest attack. Method is also known as “all-aged,” because
it maintains a mixture of three or more distinct, well-represented age classes.

Group Selection

The group selection method removes trees and establishment of a new forest crop
of young trees, or a new age class occurs in small “groups”—measuring usually a
half to 1.5 acres in size. The width of group openings is approximately twice the
mature tree height, depending on the microenvironment suitable regeneration. The
management unit or stand in which regeneration, growth, and yield are regulated
consists of an aggregation of many groups (19 in example shown). Young tree regeneration
can be from planted seedlings, natural seeding, and/or pre-existing young trees.
This uneven-aged method relies upon gentle topography and an intricate planned network
of logging skid trails to access each group, while also protecting other groups
not to be harvested at that time.

Group ‘selection with reserves’ would retain a few trees within the harvested group
opening; the retained trees are not cut to attain goals other than regeneration
within that group.

Single Tree Selection

The single tree selection method removes individual trees of all size classes, in
a pattern more or less uniformly throughout the stand. The single trees removed
fosters establishment of a just a few new young trees, and promotes growth of remaining
trees. Young tree regeneration can be from planted seedlings and/or natural seeding.
This uneven-aged method relies upon gentle topography and an intricate planned network
of logging skid trails to periodically access the entire stand area (frequent intervals),
during each harvest of a few trees, while also protecting the majority of trees
not to be harvested at that time.

Coppice methods achieve the majority of regeneration from stump sprouts or root
suckers, to generally establish and grow a stand with a single age class, or possibly
two tree canopy layers and two age classes. Oregon’s native conifer species cannot
reproduce successfully by sprouts or suckers; and neither do commercial hardwood
species. Coppice method is limited to quaking aspen management in eastern Oregon.

Coppice – All trees in the tree canopy are cut; and the majority
of young tree regeneration is from sprouts or root suckers.

Coppice with Reserves – Several reserve trees are retained in the
tree canopy to attain goals other than regeneration. The method may create a two-aged
stand.

Coppice Selection – Only selected canopy trees of merchantable
size are cut at each harvest, resulting in an two-aged or uneven-aged stand.

An
intermediate method—generically called “thinning”— is a harvest treatment with the
goal to modify the existing stand of trees, allowing for continued stand development—usually
intended to enhance the health, composition, quality, density, and/or growth of
the established leave trees. Intermediate methods cut trees (usually merchantable)
many years or decades prior to the final regeneration harvest. This method occurs
at some “intermediate” time midway during the planned entire life of the tree stand—known
as the rotation length.

Intermediate cuttings are a stand-tending phase of a silvicultural method. They
are different from regeneration methods, which are designed to remove a mature stand,
and begin establishment of young new stand of seedlings. The most common term applied
to intermediate methods is “thinning,” because to the lay-person when some trees
are removed and many other trees are retained from the same area, the forest stand
appears to be thinned.

A “pre-commercial thinning” is conducted in a sapling-size or pole-size stand of
trees, from which the size, volume and value of trees cut is too small to justify
harvest and removal of merchantable logs to mills. A “commercial thinning” is conducted
in a pole-size or larger immature stand of trees, from which the size, volume and
value of trees cut is large enough to justify harvest and removal of merchantable
logs to mills.

Intermediate methods may be more specifically characterized by their purpose. When
more than one purpose is prescribed for an intermediate cutting, the term “thinning”
is loosely applied. A thinning is a cutting treatment made to reduce stand density
of trees primarily to improve growth, enhance forest health, or recover potential
mortality. Specific intermediate methods and their objectives include the following
methods that cut and/or remove just a portion of trees in a stand:

Low thinning – Removal of trees from the lower crown classes to
favor those in the upper canopy (synonym “thinning from below”)

Crown thinning – Removal of trees from the dominant and codominant
crown classes to favor the best upper canopy trees (synonym “high thinning”)

Free thinning – Removal of trees to control spacing and favor desired
trees, using a combination of thinning criteria without regard to crown position